"Bad driver" has a wider meaning than "has a criminal record".

If that driver with a criminal record keeps their rating high enough to keep driving, what's the problem? A reformed criminal who drives safely and is pleasant to their passengers would be better than half the taxi drivers I've ever had the displeasure of dealing with

A driver with criminal record is not the same thing as a bad driver.

In many senses, being able to provide meaningful jobs to people with a criminal record is actually a service to the society. At least in my opinion, the idea of punishment is also rehabilitation, not that once you've been convicted of a crime, you could never be trusted with a job where you are in contact with other people or money or anything.

So if Uber can hire them, and even their customer feedback is positive, that is a good thing.